The present invention relates to the field of medical technology and in particular to the field of transcranial magnetic stimulation (TMS). The present invention relates to a coil assembly for transcranial magnetic stimulation, an electrode assembly and a system for transcranial magnetic stimulation.
Transcranial Magnetic stimulation (TMS) is a technique for non-invasively stimulating the human brain. In particular TMS can effect a depolarization or hyperpolarization of neurons in the brain. TMS hereby uses electromagnetic induction for inducing weak electrical currents in the brain by a rapidly changing time variant magnetic field. This enables, for example, activation of specific or general brain regions with minimal impairment of the patient or test person. TMS uses electromagnetic induction to transmit electrical energy through the scalp and skull without causing pain like direct percutaneous electrical stimulation through the skin.
For TMS, a conductive coil or magnetic coil (solenoid coil) is placed on the head or in the immediate vicinity of the head and a strong rapidly changing current is passed through the coil. This causes a magnetic field which penetrates the skull and tissue essentially unattenuated and painlessly. In order to induce a sufficiently strong current flow to depolarize neurons in the brain, the current in the coil usually starts and stops within a few hundred microseconds, or the current in the coil reverses its direction of flow within few hundred microseconds.
TMS is currently used in different forms. In so-called single-pulse TMS, a single pulse is provided to the coil. The so-called repetitive TMS (rTMS) provides a pulse train with several magnetic pulses over a defined period of time. Currently, numerous stimulation protocols with different stimulation patterns are in use. For example, in intermittent Theta Burst Stimulation (iTBS) 3 pulses with 10 milliseconds separation are triggered, and this triple pulse is repeated 5 times per second, wherein after several minutes of stimulation short pauses are provided, respectively. The protocols in use have a defined stimulation sequence that is pre-programed/predefined.
TMS can be used, for example, in medical research and for therapeutic applications in rehabilitation after stroke, neuropathic pain, tinnitus, depression or schizophrenia.
A conventional system for transcranial magnetic stimulation comprises a coil assembly and a stimulus generator that feeds the coil assembly. The coil assembly is sometimes referred to as “coil”, the stimulus generator as “magnetic stimulation unit/device”, “stimulator” or “magnetic stimulator unit”.
Such TMS systems are already commercially available. Coil assemblies include, for example, ring-shaped coils or figure-of-eight-shaped coils by The Magstim Company Ltd, UK (e.g. “double 70 mm remote control coil”) or by MagVenture, USA (“MagPro” coils). Examples of stimulus generators include the model Magstim Rapid by The Magstim Company Ltd, UK and the MagPro stimulators by MagVenture, USA. The coil assemblies can have a switch for manual triggering of a magnetic pulse by the stimulus generator. A stimulus generator can also have a trigger input for externally triggering a TMS pulse.
US 2002/0007128 A1 teaches that for reasons of patient safety and to monitor the efficacy of transcranial magnetic stimulation, it may be desirable to monitor a patient's electroencephalogram (EEG) during a TMS session. In addition to the TMS system, an EEG system is provided for the EEG measurement. The EEG electrodes are attached to the patient's scalp in a conventional way and connected to an EEG control unit. For the positioning of the electrodes on the scalp, US 2002/0007128 A1 refers to the arrangement according to the international 10-20 system.
WO 2014/139029 A1 discloses a positioning aid in the form of a positioning cap comprising alignment devices for alignment which interact with corresponding receptacles of a TMS coil assembly in order to fix the coil assembly in a desired position on the head of the test person with respect to the positioning aid. The positioning aid can have EEG electrodes. In a first step, the positioning aid/cap (without TMS coil assembly) is aligned and fixed to the skull of the test person. In a second step, the separate TMS coil assembly is aligned with and fixed to the positioning aid. A displacement of the TMS coil assembly with respect to the skull is thus prevented.
US 2002/0007128 A1 further discloses that a control system can be provided between the EEG system and the TMS system which can switch off the TMS system if necessary. A problem with TMS is that, in particular in case of strong stimulation of the patient's brain, cramping activity or a seizure may be caused by TMS. It is thus proposed to monitor the EEG of the patient and, if a cramping activity is recognized, to switch off the transcranial magnetic stimulation. It is further suggested to end the TMS if the brain of the patient is in a desired target state based on an evaluation of the EEG data.
US 2010/0210894 A1 discloses according to a first aspect, a hood-like device comprising a TMS coil arrangement and electrodes arranged in the vicinity of the coil arrangement. In an emergency situation this hood shall be placed over a patient's head quickly for terminating a seizure. According to a second aspect a helmet-like positioning aid is proposed. The positioning aid can have EEG electrodes. Similar to WO 2014/139029 A1 the positioning aid has fixation means on which a TMS coil assembly can be fixed at a defined location by corresponding fixation means. A helmet-like positioning aid to keep a TMS coil assembly in a predetermined position with respect to the user's head is also known from US 2010/0113959 A1.
US 2002/0007128 A1 further discloses that eddy currents may be induced in the metallic EEG electrodes by the TMS pulses. This can cause the electrodes to heat up. It is therefore suggested to use TMS-compatible plastic electrodes with an otherwise unchanged electrode arrangement.
WO 2014/140432 A1 also discloses monitoring of a patient's EEG during TMS for reasons of patient safety and to monitor efficacy. Since the TMS pulses can influence the EEG system, it is suggested to measure EEG data when there is no TMS pulse, e.g. immediately after a TMS pulse.
In Zrenner et al. “Brain-state dependent brain stimulation: Real-time EEG alpha band analysis using sliding window FFT phase progression extrapolation to trigger an alpha phase locked TMS pulse with 1 millisecond accuracy”, First International Brain Stimulation Conference, 2-4 Mar. 2015, a previous publication by the inventors, it is described that a real-time electroencephalogram can be used for brain state dependent brain stimulation. This is also referred to as “EEG-TMS”. To determine the brain state, a conventional EEG is measured in real time and the activity of the alpha waves is determined. For the positioning of the EEG electrodes on the scalp, an EEG cap is used so that the electrodes are arranged at defined positions and comparable results can be achieved. The phase position of the alpha waves is determined by means of a moving FFT window. Based on the detected phase position, the transcranial magnetic stimulation is triggered synchronized in phase.
Disadvantages of the above-mentioned solutions are the high complexity of the systems and the relatively complicated handling, including the long period of time required for setup, so that their use in everyday clinical practice does not appear to be practical in many cases. A doctor could therefore be inclined to prefer drug treatment over the use of a TMS system.